What is Variable in Java?
The variable is the basic unit of storage which holds the value while the program is executed. We can also say that it is a name given to the memory location. A variable is defined by data-types provided by Java.
It may be string, int, float, char, and boolean.
Declaring a Variable in Java:
Certain rules are needed to be followed before declaring the variables:
- The first character must be a letter.
- A variable name can consist of letters A-Z, a-z, digits 0-9, and two special characters such as underscore(_) and dollar Sign($).
- Blank spaces cannot be used in variable names.
- Java keywords cannot be used as variable names.
- Variable names are case-sensitive.
Syntax to declare Variables:
1 | data_type variable_name = value; |
Here, data_type means one of the Java data-types mentioned above. variable_name is the name that must be assigned to it, you can give any name suitable for it. The equal sign(=) is an assignment Operator used to assign the value of R.H.S. to L.H.S.
Example: Demonstration of assigning value to different data-types
1 2 3 4 5 | int num = 20; String name = "Daniel"; float floatNum = 7.98f; char alphabet = 'D'; boolean bool = true; |
Types of Variables in Java:
- local variable
- instance variable
- static variable
Following declaration help us to understand the position of each of these three variables:
1 2 3 4 5 6 7 8 9 10 11 | class Example { int Num1 = 30;//instance variable static int Num2 = 40;//static variable void method_Name() { int num3 = 60;//local variable } } |
1. Local Variable:
A variable that is declared within the body of the method or constructor is called a local variable. This variable is used only within that block or method where it was created other classes cannot access it. And is destroyed after exiting the method or block. Initialization of Local Variables is necessary.
Example of Local variable in Java:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | public class Employees { public void EmployeeInfo() { // local variable age int age = 0; String name = "Prashant"; age = age + 30; System.out.println("Employee age is : " + age); System.out.println("Employee name is : " + name ); } public static void main(String args[]) { Employees emp = new Employees(); emp.EmployeeInfo(); } } |
Output of local variable in Java:
1 2 | Employee age is : 30 Employee name is : Prashant |
2. Instance Variable:
These are the non-static variable that is declared within the class but outside the method or constructor. With the creation of Objects, Instance Variable is created and destruction of an object destroys the variables. And can be accessed only by creating objects. Initialization of Instance Variable is not necessary as it is 0 by default.
Example of Instance variable in Java:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | public class Employees { // this instance variable String name; int age; public Employees (String EmployeeName) { name = EmployeeName; } public void EmpAge(int EmployeeAge) { age = EmployeeAge; } public void Display() { System.out.println("Employee name: " + name ); System.out.println("Employee age :" + age); } public static void main(String args[]) { Employees r = new Employees("Prashant"); r.EmpAge(20); r.Display(); } } |
Output of Instance variable in Java:
1 2 | Employee name: Prashant Employee age :20 |
3. Static variable:
These variables are also known as class Variables. These are declared just like Instance Variable that within the class but outside the constructor or method but the difference is that static variable is declared using static keyword. Unlike Instance variable, only one static variable is created its value remains the same for all objects no matter how many objects user creates. Here initialization is not mandatory, it is 0 by default.
Example of Static variable in Java:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | public class Employees { //static variable static int id = 1101; public static void main(String[] args) { Employees emp = new Employees(); // Call static variable using object reference variable int a = emp.id; System.out.println("Employee ID: "); System.out.println(Employees.id); } } |
Output of Static variable in Java:
1 2 | Employee ID: 1101 |